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Resource or Project Abstract

In this study, predefined exposure periods and subsequent laboratory extractions were compared with high-resolution data sets for total oxidisable nitrogen, total phosphorus and total reactive phosphorus that were collected at established monitoring stations. Multiple cartridges were deployed on 14 occasions in a variety of river systems in an effort to rigorously validate their use in rivers. These transfer risk patterns are summarised as showing indications of high P or N in storm flows and/or in inter-storm periods and from a variety of point and diffuse sources, the latter from both lateral (P) and vertical (N) flows. This allowed the accurate determination of time- and flow-weighted mean concentrations for the sampling periods that ranged from 3 to 5 weeks. A departure from the original systematic experimental design (a single river system, multiple deployment periods) occurred due to emerging factors relating to variable and under-estimation of flowweighted mean concentrations. Hence the deployment strategy was extended to a number of river systems with different hydrological responses and nutrient transfer risks to ensure that any issues were not related to one particular site. Variability existed in the P and N concentrations returned by the cartridges compared to those measured by the high-resolution monitoring equipment. It included under- and over-estimates of nutrient fluxes (as flow-weighted mean concentrations) from near-continuous time series data. Experiments were subsequently conducted to investigate the discrepancies that existed between passive sensor results and high-resolution data. Hydrodynamic simulations were conducted using a two-dimensional lattice Boltzmann discrete element methodology. This allowed fluid movement around the cartridge to be modelled as discrete particles, and simulations demonstrated flow divergence round the cartridges rather than into them. Issues were raised regarding the accumulation of detritus around the cartridges during storm events, the effectiveness of the cartridges during low flow, and the implications of invertebrate and algal colonisation. To test adsorbance and tracer salt loss, and to eliminate external environmental variables, cartridges were exposed to standard solutions of known (P and N) concentration and ambient river samples via controlled pumping. Concentrations of P and N determined by cartridges in the pump test trials still displayed discrepancies in comparison to actual concentrations determined by standard methods in the river samples. However, estimation of cartridge throughflow using tracer salt dissolution rate appeared to be a reliable methodology, but only when flow was forced through the cartridge under pumped pressure. The issues of temporal coverage for chemical monitoring in rivers remain highly important for future evaluation of catchment policy measures. Multiple factors have been highlighted regarding the performance of the cartridges and their variable recoveries when compared with flow-proportional data. Further investigation into these factors would allow the true effectiveness of the passive sensor cartridge to be quantified in Irish river systems and informed adaptations made to the cartridge design to improve function. As these issues become resolved, the passive system could be extremely useful to the WFD authorities mentioned above, in tandem with current monitoring programmes, and possibly form part of a complementary suite of smart infrastructure for ongoing and future water monitoring programmes.

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Number of Attached Files (Publicly and Openly Available for Download):

2

Project Start Date

Tuesday 1st January 2008 (01-01-2008)

Earliest Recorded Date within any attached datasets or digital objects

Tuesday 1st January 2008 (01-01-2008)

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Geographical and Spatial Information Related To This Resource

Description of Geographical Characteristics of This Project or Dataset For field monitoring, the main station used in this project was a 5 km2 sub-catchment of the Blackwater River in Co. Monaghan. These data were augmented by a similar station in Co. Tyrone, also a 5 km2 subcatchment of the Blackwater River. Both sites were part of a previous large-scale project, Blackwater TRACE (Jordan et al., 2008). These two sites were typical of flashy drumlin hydrological systems with both point and diffuse pressures, typically with high P and low N background and storm concentrations. Subsequent to the start of the project, a number of other sites were used that had the potential for: high P and high N concentrations (part of the Dee system in Co. Louth); low P and high N concentrations (part of the Slaney system in Co. Wexford); and low P and low N concentrations (part of the Robe system in Co. Mayo); see Fig. 2.1. Each site had hydrometry and waterquality instrumentation measuring discharge, P and N on a sub-hourly basis

Supplementary Information About This Resource

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Lineage information about this project or dataset

The Environmental Protection Agency (EPA) is the statutory authority in Ireland for the protection of the environment. Along with other competent authorities, such as the River Basin Districts and local authorities, the EPA is charged with monitoring the ongoing chemical and biological state of water bodies. This is in alignment with the implementation of the Water Framework Directive (WFD; Official Journal of the European Community (OJEC), 2000) and the associated programmes of measures. Rivers, for example, which can be spatially and temporally variable, require monitoring networks that are extensive and are potentially an expensive commitment. In Ireland, spatial coverage has been favoured over temporal coverage in many monitoring programmes. However, as chemical pollutant transfers can be related to short-term discrete events or events related to storm hydrology, absence of a temporal emphasis to monitoring may result in an under-representation of these types of transfer from As phosphorus (P) and nitrogen (N) transfers are considered to be persistent in Irish catchments, from multiple point and diffuse (including domestic and agricultural) sources, the purpose of this research project was to validate a commercially available passive flow-proportional sampling solution for P and N in Irish rivers. This is especially pertinent in the context of the WFD objectives of achieving and/or maintaining good status. Moreover, the project aims were to test an alternative to discrete grab sampling in rivers for nutrient concentrations using an approach that purported to give a more representative, integrated concentration over a deployment period, ideally synonymous with flowweighted mean concentrations.

Supplementary Information

The passive sampling systems would be extremely useful to research and statutory agencies monitoring water quality for P and N transfers. Recommendations arising from this project are that further research and development are required to fully address the issues raised in this report regarding the use of flow-proportional passive samplers in Irish rivers. Multiple factors have been highlighted regarding the performance of the cartridges that appear not to perform in a flow-proportional manner and therefore do not return appropriate recoveries of P and N concentrations as compared with high-resolution data sets. These interacting factors are: ? Flow divergence; ? Loss of flow/velocity-proportional nutrient adsorbance; ? Loss of throughflow; ? Debris build-up at cartridge interface due to deployment methodology; ? Speculated biological interference on a physical and chemical level; ? Laboratory elution and recovery of nutrients (possibly also influenced by laboratory methods). Further investigation into these factors would allow the effectiveness of the cartridges to be quantified in Irish river systems and informed adaptations made to the cartridge design to improve function, including deployment to ensure unobstructed throughflow and anti-biofouling. However, research into the developmental issues surrounding the InStream passive system was not part of this project outline or within the remit of the EPA STRIVE

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a similiar thematic area to the resource Flow-proportional Passive Sensor Validation of Phosphorus and Nitrogen in Irish Rivers (Flow-Pro) you are currently viewing. You can view the
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